Field of Invention
This invention relates generally to a method for enhancing the properties of a layer of open-cell foam plastic material, and more particularly to a method in which the cells of the layer are impregnated with filler particles that impart the desired properties to the layer.
In my above-identified copending application, there is disclosed a flexible, open-cell polyurethane foam product having acceptable dielectric heat-sealing characteristics. To further enhance the dielectric heat-sealing characteristics of the open-cell polyurethane foam product, the product is saturated or permeated with thermoplastic powders such as PVC having a dielectric loss index greater than that of polyurethane.
The concern of the present invention is with the enhancement of certain properties of an open-cell plastic foam layer or product other than its dielectric-heat sealing properties.
The property enhancement of interest may be the mechanical properties of the plastic foam layer, or the thermal or electrical insulation or conductivity properties thereof. Thus, as indicated in the article by Vance Staymer, "Non Fibrous Property Enhancers," which appears in the 1983-1984 edition of the Modern Plastic Encyclopedia (pages 125 et seq.), a mix of magnesium sulfate and other non-fibrous materials can be used to impart fire retardance or smoke suppression characteristics to plastic building panels.
The term "non-fibrous" filler materials includes high-density silica sands and hollow glass spheres. Carbon, metal powder, or silver-coated glass spheres can be used as electrically-conductive fillers in plastics to carry off static electricity and to provide electromagnetic shielding.
Where the filler particles are intermixed with the plastic resin in the slurry state, this process is feasible if the particle sizes are small. Or the filler particles may be intermixed with resin particles which are then rendered molten and injection molded or extruded to form plastic products in which the filler particles are dispersed.
But in producing a synthetic plastic, open-cell foam product, the foam-forming reactive mixture contains a foaming agent and a reaction catalyst; hence the addition of a particulate filler to the reactive mixture may, depending on the physical and chemical nature of the filler particles, interfere with the foam-forming process or impair the quality of the product.